Means for adjusting oscillation period of exhausts of internal-combustion engines



May 14, 1929. H. H. MAXIM 1,713,047

MEANS FOR ADJUSTING OSCILLATION PERIOD OF EXHAUSTS OF INTERNAL COMBUSTION ENGINES Filed Nov. 14, 1924 INVENTOR ATTORNEYS Patented May 14, 1929..

UNITED STATES PATENT OFFICE.

111m HAMILTON Maxim, or HARTFORD," connncrrou'r, ASSIGNOR, BY MESNE AS- SIGNMENTS, TO THE MAXIM .SILENCERICOMIPAINY, or HARTFORD, CONNECTICUT,

A CQIRPORATIOH OF CONNECTICUT.

rims non ADJUSTING OSOILLATION ,PE-R'IOD or EXHAUSTS or INTERNAL-COMBUS- v TION ENGINES.

Application m d November 14, 1924. Serial No. 750,013.

This invention relates to improvements in methods and apparatus for silencing the exhaust of an internal combustion engine with a minimum of back pressure.

The efiiciency of a combustion engine depends to a' large extent upon its ability to be relieved of its burned gases, that is to say, such "an engine will develop more or less power according to the extent that it is scavenged of its dead gases. It is usual to.

- use, in connection with such engines, some type of silencer or pipe coupled to theexhaust port which conducts the gases from the engine, but due to a misconception ofthe requirements of such silencers and a consequent improper designing thereof, the pipes or silencers heretofore employed are not suitable for conducting all of the gases-from the engine and there results a considerable back pressure and an incomplete scavenging of the cylinder, which tends, most. naturally, to impair theefiiciency of the engine.

. The present invention, relating to silencers, aims to take advantage of the fact that the exhaust gas pulse ofan engine instead of consisting of a single sustained pufi at a pressure greater than atmosphere, is, on the I contrary, in the nature of a rapidly oscillating pressure alternating between relatively high and low pressures. This may be termed a pressure wave oscillating at high frequency between a comparatively high pressure above atmosphere and a relatively low pressure that may be below atmosphere.

. In the-carrying out of my invention. I arrange the timing of the frequency of the oscillations of pressure with respect to the closing of the exhaust port of the engine so that its closing coincides with a low pressure period of the pressure wave, since at that period there will be aminimum of back pressure in the cylinder and a resulting approximately complete scavenging thereof. The

lower the pressure at whichthe port is closed.

the more complete will be the scavenging of the cylinder and, as previously stated, it has been found to be desirable to time the closing of the port to coincide with some low pressure period to obviate, as faras'possible,'all back pressure. v

However, due to the comparatively high frequency of the so-called pressure oscillations and to the mechanical impracticability ofvarying' the timing-of the exhaust port closing in relation to one of the lower pressureperiods, I provide a novel method and apparatus for varying or controlling the wave length or frequency of the said pressure oscillations so that they may be timed to have a low pressure period that will coincide with the predetermined closing of the exhaust port. This may be accomplished by the provision of means for varying the physlcal proportions of the exhaust gas passageway, which passageway, according to my invent-ion, may have its length or volume varied or controlled to thereby vary the physical proportions as above stated. I also .find it practical to embody the principles of my invention in a' muffler or silencer for the engine so that the double function-may be performed the provision of a. novel method and apparatus capable of producing the desired results and which is applicable to any and all types of combustion engines now in use.

Other objects and advantages will be apparent from the following description and accompanying drawings, in which is illustrated various forms of apparatus for practicing the invention, and it will be understood that various other embodiments may be employed to accomplish the desired results.

In the drawings:

Fig. 1 is a sectional elevational view through a frequency changing apparatus embodying the principles of my invention;

Fig. 2 is a sectional plan view taken on the line 22 of Fig. 1;

Figs. 3 and 4 are diagrammatic representations of an indicator chart which graphically represents the relative pressures Within a combustion engine cylinder during a complete cycle or stroke of the piston.

The apparatus now to be described is only intended to enable those skilled in the art to practice the invention and various other S that is supported, as shown, and held in a rigid relation with respect to the engine. The silencer S may comprise lower and upper headers 2 and 3 that are secured to a shell 4,

thus roviding a cylindrical shell-like strucbest shown in Fig. 2. The inner turn of the spiral wall circumscribes the inlet port 5 at the bottom header 2, while the wall 9 of the casing and bottom header 2 of the silencer close the spaces between the turns of the spiral so that a passageway 11 is provided t at extends spirally from the center port 5 to the outer periphery of the casing. The

scroll member is preferably secured in the position shown and normally conducts the exaust gases spirally and outwardly from the port 5 to the interior chamber 8 of the shellf A half cylindrical or semi-circular member M is provided that is adapted to partially encircle the member M, as best shown in Fig. 2. The said niember M is arranged for a free rotative movement about the casing M and is supported by rollers 12 that ride upon a circular track 13 extending upwardly from the bottom header 2.

A shaft 14, carried for a rotative movement in a side of the shell 4, has fixed to its outer end a crank handle 15, while its inner end has fixed thereto a pinion gear 16 that engages with a the member'M'. This mechanism is adapted and arranged so that a rotation of the crank handle will rotate the member M with respect to the casing M and'thereby vary the length of the passageway 11 and consequently vary or controlthe total length of the exhaust conduit for the exhaust gases.

As shown in Fig. 2, the spiral passageway 11 opens into the chamber 8 at V and the arrangement providesfor varying the position of this opening through almost 180 to approximately the point Y. This variation of the spiral discharge opening with consequent variation of the length of the spiral passageway 11 makes possible a sufficient range of adjustment to take care of the natura period of oscillatory pressure discharge from the ordinary engine and to so vary its wave length that a time of low pressure will coincide with the closing of the engine exhaust ort. v

In escribing the operation of the apparatus, reference will first be made to the indicator diagram represented in Fig. .3, which shows the relative pressures within a combustion cylinder during one complete cycle 'haust pipe and mufiier connections such conditions.

circular rack 17 carried by of operation. The compression stroke, as will be seen, is represented on the lower side of the diagram at C, the combustion period at C and the exhaust period at X, the point 0: indicating the opening of the exhaust valve, while G represeitts the intake or charging period of the flirohe or cycle. It will be observed that during the combustion stroke C and the exhaust stroke X, the pressure alternates in the form of oscillations between relatively low and high pressure periods-as previously explained, and since we are not concerned with the variations during the combustion stroke, that part X of the curve, showing the various in pressure during the exhaust period, is represented at a larger scale in Fig. 4. In this diagram, the vertical axis 0-a is a measure of pressure and the horizontal axis 0a a measure of time divided into units 6. It is assumed that the closing of the exhaust port of the engine occurs at the point 3 The pressure wave of the exhaust, illustrated in this view, may be assumed to have the natural period caused by usual exand before any adjustment thereof is made. It will be observed that the closing of the exhaust port under such conditions does not coincide with a low pressure point in said wave as indicated by the dotted line y-y. Only fair scavenging of the engine would result from A much worse condition might occur if the line y y' intersected the crest of a wave, and obviously the best conditions for scavenging would result from so increasing the wave length (distance from that the trough y" of a wave would be intersected by the line y-gy': This would mean that the exhaust would close at a period of low pressure, perhaps even below atmospheric pressure, when the engine would be most completely scavenged of its dead gases.

crest to crest) of said oscillatory discharge While I have shown apparatus of a certain structure for varying the length and volume of the exhaust pamageway, it will be obvious that any other apparatus desired may be employed that will function in a like manner, and I therefore prefer not to be limited by the foregoing description, but rather by the appended claims.

'What I claim is:

1.. The combination with an internal combustion engine of a silencer for'the exhaust of said engine cbmprising, a scroll member.

providing a spiral passagewa of several convolutions formed of concentric wall portions, 9. movably mounted concentric wall ortion overlapping the outermost wall of sai scroll member, and means to adjust said movable wall portion about the axis of said scroll member to vary the length of said spiral passageway. y

2. The combination with an internal combustion engine of means for reducing the back arranged exhaust passagewa pressure of the exhaust comprising a spirally of adjustable dimensions and means for e ecting gradual variation in said dimensions so as to vary the frequency of the exhaust pressure wave:

3. The combination with an internal combustion engine of a silencer for the exhaust of said engine comprising a scroll member providing a spiral passageway and having an adjustable portion for varying the length of said spiral passageway, and means for adjusting the same whereby the oscillation fre quency of said exhaust pressure wave may be controlled.

4. The combination with an internal combustion engine of means for reducing the back pressure of the exhaust comprising a spirally arranged exhaust passageway of adjustable dimensions and means for efiecting a gradual variation in said dimensions so as to vary the frequency of the exhaust pressure wave whereby the closing of the exhaust valve of said engine takes place simultaneously with the arrival of a low pressure region in said exhaust pressure wave at said exhaust valve.

'5.'The combination with an-internal com- In testimony whereof I have afiixed my signature.

HIRAM HAMILTON. MAXIM. 

